The article by Van Jacobson et al. entitled “Networking Named Content”, published in 2009 in the proceedings of the CoNEXT'09 conference, presents a new architecture called Content-Centric Networking (CCN). This architecture proposes to change the current communication model based on physical addressing in a network by a new communication model based on addressing by content name. In such a network, the idea is therefore to propose, find and deliver content rather than reaching equipment devices and maintaining connections between these equipment devices.
In order to obtain a content in such a network, a client entity sends in the network a request relating to this content and comprising the name of the content. Such a request is referred to as an interest packet. On reception of this request on a given network interface, a forwarding node of the network, or CCN node, checks whether it has the desired content. To this end, it consults a table of contents which it contains and which stores contents. If it has the desired content, it sends it to the network interface via which the request was received, to the client entity, optionally via other forwarding nodes of the network. If it does not have the desired content, it checks in a pending interest table (PIT) whether it has already received a previous request relating to the same content via the same interface or another interface and sent the previous request to other forwarding nodes of the network. If this is not the case, that is to say if it finds no trace of a previous request relating to the same content in its pending interest table, it stores the name of the desired content in its pending interest table in association with an identifier of the interface via which the request was received. It subsequently forwards the request in the communication network by means of a forwarding information base (FIB) which it has and which indicates, as a function of the requested content name, to which other node or nodes of the network to transfer the request. If, however, its pending interest table PIT already comprises the name of the desired content in association with the identifier of another interface, it does not send the received request but instead, in its pending interest table PIT, associates with the name of the desired content an identifier of the interface via which the request was received. This is because, if the pending interest table already comprises the name of the desired content, this means that a request relating to this content has previously been received and transferred in the network, and that the node is waiting for a response to this request.
The pending interest table PIT thus stores the names of the requested contents in association with the identifiers of all the interfaces through which the content has been requested, and should therefore be sent in response.
When a content is received on a given interface by the forwarding node, after a request relating to this content has been sent by this node, the node then consults its pending interest table and sends the content over all the interfaces which are associated with the name of the content. The pending interest table therefore makes it possible to find the path which a content should take in order to reach the client entity or entities which have requested it.
In this known architecture of CCN nodes, the contents are organized hierarchically in a tree form. The name of the content takes this organization into account. For example, /orange/map/lannion/site/batWA.jpg and /orange/map/lannion/site/batWB.jpg are two content names which share a common tree location, in this case /orange/map/lannion/site/. It can be seen that the name of a content is of variable size, depending on the size of the tree location in which the content is located. In order to process an interest packet, a CCN forwarding node must therefore store and handle content names represented over an arbitrary number of bits as well as the identifier of the interface, or identifiers of the interface, on which the interest packets were received. The pending interest table PIT of a CCN node, which stores all the received interest packets as well as the information relating to the path which the content must take, may then constitute a weakness of a CCN network because of the size which this table may reach. In fact, since CCN networks are intended to forward all the content made available on the Internet, it will be understood that such a table may store megabytes or even gigabytes of information. It is moreover known that the larger the size of the pending interest table is, the longer are the access times to the data which it contains. This can significantly impair performance of a CCN network.